B. TECH DEGREE
EXAMINATION, MAY 2012
MODEL QUESTION
PAPER
FIFTH SEMESTER
CE 010504
GEOTECHNICAL ENGINEERING
Time: Three
Hours Maximum Mark: 100
(Answer All
Questions
Graph /Semi log
Sheets to be supplied
Missing Data if
any, may be suitably assumed)
PART A
(Answer All Questions)
1.
Differentiate between Void ratio and porosity of soil. Give the relationship
between them.
2. What is critical
hydraulic gradient? Mention its significance.
3. What is Mohr’s circle? What is its important
characteristics?
4. What is Taylor’s Stability number.
5. Define over consolidated, normally consolidated
and under consolidated soil.
(5x3 = 15marks)
PART B
(Answer All Questions)
6. Sketch
neatly the IS Plasticity Chart. Mention its use in soil classification.
7. Briefly explain the factors affecting
permeability.
8. What is liquefaction of sand? How can it be
prevented?
9. Explain one method of field compaction control.
10. Discuss the spring analogy for primary
consolidation.
(5x5 = 25marks)
PART C (12 marks each)
Module I
11 (i) Obtain the relationship between void
ratio, water content and specific
Gravity for a partially
saturated soil. (6marks)
( ii) A moist soil weighs 10.1 N and has a
volume of 800 cc. Its dry weight is
9.18 N. Determine the void ratio, porosity,
moisture content and degree of
saturation. Take unit weight of water as
9.81kN/m3and specific gravity
G = 2.65 (6marks)
OR
12 (i)Explain the important three clay
minerals. (6marks)
(ii) Calculate
the flow index, plasticity index and toughness index of a soil sample from the
following data obtained while conducting the liquid limit test. Plastic limit
of the soil may be taken as 25%.
Number
of blows
|
8
|
20
|
32
|
45
|
Water
content(%)
|
70
|
60.2
|
53.4
|
50
|
(6marks)
Module II
13.
At a construction site, a 3m. thick clay layer is followed by a 4m. thick
gravel layer, which is resting on an impervious rock a load of 25 kN/m2
is applied suddenly at the surface.The saturated unit weight of the soil are
19kN/m3 and 20kN/m3, for the clay and gravel layers respectively. The water
table is at the ground surface. Draw
diagrams showing variation with depth of total, neutral and effective stress in
the layers. (12marks)
OR
14. (i)Explain the different properties of flow
net (6marks)
(ii)A soil sample 90mm. high and 6,000 mm2
in cross section was subjected to a falling head permeability test. The head
fell from 500mm.to300mm.in1500sec.The soil has a permeability of 2.4 x 10-3mm/sec.
What is the diameter of the stand pipe. (6marks)
Module
III
15.
(i)Briefly discuss the Mohr Coloumb failure theory. Also, give the relationship
between principal stresses at failure (6marks)
(ii)In a triaxial test conducted on a soil
sample having cohesion of 12 kN/m2 and angle of internal friction of
25°,the
all- round fluid pressure was 200 kN/m2.What should be the value of
deviator stress at failure. (6marks)
OR
16 (i)A shear box test on
clean sand gave a failure shear stress of 70kPa when the normal stress was 200 kPa.Draw
the Mohr circle and Mohr envelope and find the principal stress at failure and
the orientation of the principal planes.
(6marks)
(ii) How do you obtain shear
strength of soft clays using Vane Shear Test. Derive the formula to be
used.
(6marks)
Module IV
17. (i)Explain standard
compaction test. How is it different from heavy compaction test
(6marks)
(ii)Explain the effect of compaction on the engineering properties of
the soil .Explain briefly. (6marks)
OR
18 (i)A foundation trench
with vertical slopes has to be excavated in a cohesive soil. The cohesive
strength of the soil is 25kN/m2.and the angle of shearing resistance
is 10°.The unit weight of the soil is 19.4 kN/m3. The
magnitude of stability number is 0.22 for slope angle = 90° and the angle of
shearing resistance =10°. What is the depth of foundation trench
if the F.S is 1.5.
(6marks)
(ii Explain briefly the Swedish Circle
method, Ø=0 analysis. (6marks)
Module
V
19. (i)Using Terzaghi’s one
dimensional theory of consolidation, derive the differential equation for
consolidation. State the assumption used. (6marks) (ii) A
building is constructed over a 4 m. thick clay layer which is sandwiched
between sand layers.Compute the time required for 50% consolidation of clay if
its coefficient of consolidation is 0.02cm2/min. (6marks)
OR
20. A saturated soil stratum
5m. thick lies above an impervious stratum and below pervious stratum. It has
compression index of 0.25 and coefficient of permeability of 3.2x10-10m/s.Its
void ratio at a stress of 147 kN/m2 is 1.9. Calculate (a) Change in void ratio
due to increase of stress to 196kN/m2 (b)Coefficient of consolidation
(c)coefficient of volume compressibility and (d) Time required for 50%
consolidation (Tv=0.197) (12marks)
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